Radio spectrum monitoring apparatus



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Febo '21, E950 GEW@ QNGW WCHA/QD c. @A wwe/v0 Patented Feb. 7, v1950UNITED STATES PATENT OFFICE RADIO SPECTRUM MONITORING APPARATUS RichardC. Raymond, State College, Pa., assigner `to the United States-ofAmerica as represented bythe Secretary of War 6 Claims.

`This invention relates generally to electrical apparatus and moreparticularly to a radio frequency receiver.

yIn many cases, such as in the operation of nete works controlled by amaster transmitting station, it is desired to set a transmitterfrequency 'exactly on that of another transmitter whose signal isreceived. The accuracy with which a local transmitter may thus be Aseton the frequency of a received signal by the use of an audio frequencyindicator is dependent in part upon the modulation ofthe receivedsignal. As

aural setting becomes increasingly diiiicult and inaccuracy generallyresults. The spectral distribution of energy in a pulsedy signal is sobroad kthat in most cases it renders aural setting irnpractical and thetransmitter can be set more nearly on the desired frequency when thespectrum of the received energy is presented on a visual indicator.

` It is an object of this invention to provide a radio frequencyreceiver which will accurately determine the carrier frequency of areceived signal.

onthe frequency of a selected received signal.

This invention is therefore designed to combine the properties .of `abroad-band search receiver, and a narrow band spectrum analyzer withvisual presentation, in order that the spectrum of the "received signalmay be investigated and in order that the frequency `of alocalorothertransmitter may be set in the center on any desired part of thespectrum.

A received signal is mixed with the frequency of the local receiveroscillator and the resulting frequencies are passed through a relativelybroad-band intermediatedrequency amplifier.

the spectral distribution of energy broadens,

The output from this amplifier is divided, part of the energy istransferred to the detector and audio amplifier circuit and theremainder passes into a relatively narrowband intermediateffre quencyamplified, the frequencies passed by this amplifier are impressed on acathode ray oscil loscope for visualpresentation.

Other objects, features. and advantages of this invention will suggestthemselves to those skilled in the art and will become apparent from'the following description of the invention taken 'in connection withthe accompanying drawing which is a block diagram of a'freceive'rembodying the principles of the present invention Referring new to thedrawing, it is'seen that a mixer stage IB, has its 'input circuitconnectedito an antenna il and its output circuitconnected to abroadeband 'intermediate frequency stage l2. Amplifier stage l2 feeds asignalto detector and audio-frequency amplifierstage i3 whose outputoperates an aural device such asheadphones I4.

.Amplifier l2 also feeds a signal to lnarrow-'band intermediate4frequency amplifier I5 whose output is presented on acathode-ray-'oscilloscope F6. An adjustable frequency-rnodulator ll'feedsa lsignal v'to local oscillator I8 whose youtput isfed'to mixerstage ll-i'l. Adjustable frequency-modulator stage il also feeds'asignal'to a sweep circuit 19 which-provides sweep voltages forcathode-rayoscilloscope I6.

The device herein :disclosed consists ofy a super heterodyne typereceiver equipped with broad' band Vcircuits followed by anauralindicator for use as a search receiver. Narrow bandy circuits followedby a visual indicator are also included in the/device for the rpurposeof accurately setting a locally transmittedfrequency to that of thereceived signal.

As shown by the drawing the local oscillator 'i8 is frequency modulated.The' frequency deviation is Tata iixedsuita'ble rate and the extent ofthe r`frequency deviation is adjustable. vThe sweep circuit I5 `of thecathc'deeray-oscilloscope is synchronized with 'the frequency excursionsof vthe local oscillator it. The pass-band `of the narrow-band amplifierl5ris centeredat a 'frequency `in the lower part of the passbandiof 'thebroad-band amplifier l2 in order that the dual signal rdetected by thereceiver may be presented on the oscilloscope with lminimum frequencydeviation of the local oscillator; thus preventing ambiguity concerningthe dual signal.

`For example, assume 'they broadeband amplifier 'IZ't'o 'pass"frequenciesbetween `l5 and 20 megacycles and the narrow-band amplifierl5 to pass frequencies between l5 and 16 megacycles. Suppose thereceived signal to be at a frequency of 560 megacycles, then a doublesignal would be visible on the oscilloscope when the local cscillator istuned to a frequency of 575.5 megacycles 3 4 and when tuned to afrequency of 544.5 megacoupled to the output of said mixer', one channelcycleshaving a pass band which is wider than that of Thus, by way ofexample, if the frequency the other channel and having means for audiblydeviation of the local oscillator I8 due to fre translating themodulation component of a wave quency modulation is 32 megacycles ormore, it 5 therein, the center frequency of said other chanis possibleto present two presentations of the nel being displaced from the centerfrequency of signal on the oscilloscope screen simultaneously. said onechannel but within the pass band there- Now if the frequency of a localor other transof, means to vary the frequency f Said Oscillator mitteris adjusted until its signal responses as over a range equal to at leasttwice the center shown on the oscilloscope are coincident with the l0frequency of Said Othei channel whereby e beet similar responses fromthe received signal, frefrequency within the pass band of said otherquency coincidence of the two signals will be Channel will be derivedfrom a given incoming achieved. Wave at two diierent frequency settingsof said While there has been here described one emoscillator, and meansresponsive to the output of bodiment of the present invention, it willbe man 15 Said other channel to provide a Deir of spaced ifesi; to thoseskiued in the am; that various visual indications dependent upon saidtwo difchanges and modications may be made therein. ferent settings.

It is therefore aimed in the appended claims to In a radio SeelChreceiver adapted to transcover al1 such changes and modifications asfall late the modulation component and indicate a within the true spiritand scope of the invention. frequency Characteristic Ol WeVeS Within eDle- What is Claimed is; determined frequency region, a localoscillator,

l. In a network adapted to translate waves of e. IniXeI OI hetelodyningSaid WeVeS With the a, given frequency, an oscillator, a mixer forOutput Of Said OSClllEttOl 't0 derive a dlerenceheterodyning said wavewith the output of said frequency wave, a pail' ci tuned channelscoupled oscillator to derive difference-frequencies, a t0 the Output 0fSeid miXel, One Channel having Channel Xedly tuned in the region 0f a,predea pass band which is wider than that of the other termineddifference-frequency and coupled to the Channel and having Ineenstherein fOl alldibly output of said mixer, means continuously and petranslating the modulation component of a wave, riodically varying thefrequency of said oscillator the Centel frequency of said other channelbeing over a range extending at least from the redisplaced from thecenter frequency of said one quency of said waves minus thepredetermined channel but within the pass band thereof, meansdifference-frequency to the frequency of said t0 modulate the frequencyof said oscillator over waves plus the predetermined difference-freySuch a range that a beat frequency within the quency and signalindicating means coupled to pass band of said other channel will bederived the output of said channel. from a given incoming wave at twodifferent fre- 2. A receiver for waves within a predetermined (lllenCeS0f Seid OSciletOl', e Cathode ley Oscillofrequency region comprising anoscillator having Scope, ineens l'eSpOnSiVe t0 the Output 0l Said a meanfrequency which is substantially equal to other channel to deflect thebeam of said oscili-,he mean frequency of Said regiony a mixer forloscope along one coordinate, and means to deheterodyning said waveswith the output oi said 40 neet the beam Of Said Oscilloscope along aSecond Osciuator to derive .diereneafrequencieg a coordinate insynchronism with modulation of xed1ytuned intermediatefyequency @hannasaid oscillator, whereby two indications spaced by sharply tuned to apredetermined difference-frean amount proportional to two frequencieswill quency and coupled to the output of said mixer, be DlOVCled by Saidincoming Wave.

means to continuously frequency modulate said 6. In a receiver as setforth in claim 5, wherein oscillator over a range equal to twice saidpredethe DeSS hand of Said other channel is in the termineddifference-frequency, and indicating Vicinity 0f the lOWeT frequencylimit Of Said one means coupled to the output of said channel. Channel.

3. In a search receiver adapted to indicate the RICHARD C. RAYMOND.frequency characteristic of waves within a predetermined frequencyregion, a local oscillator, REFERENCES CITED a mixer for hetercdynngSeid WeVeS With the The following references are of record in the outputof said oscillator, a Xedly-tuned channel me 0f this patent; coupled tothe output of said mixer, means continuously frequency modulating saidoscillator UNITED STATES PATENTS over such a range that a beat frequencywithin Number Name Date the pass band of said channel will be derived2,099,156 Wheeler Nov. 16, 1937 from a given incoming wave at twodifferent fre- 2,387,685 Sanders Oct. 23, 1945 quency settings of saidoscillator located on opposite sides of the mean frequency of saidrange, FOREIGN PATENTS and means responsive to the output of said chan-Number Country Date I nel to provide a pair of indications dependent101,039 Australia May 1l, 1 37 upon said two different frequencysettings.

4. In a search receiver adapted to detect and OTHER REFERENCES l iindicate a frequency characteristic of waves Radio, March 12, 1942, pp.15-18, i6-49, by R. within a predetermined frequency region, a localPopkin-Clurman, Panoramic Radio Reception. oscillator, a mixer forheterodyning said waves Electronic Industries, July 1944, pp. 86, 87,88, with the output of said oscillator to derive a dif- 106, Article,Panoramic Principles, by Moulic. ference-frequency wave, a pair of tunedchannels

